Process of reducing sugars to alcohols



H. J. CREIGHTON 1,990,582

PROCESS OF REDUCING SUGARS TO ALCOHOLS I Feb. 12, 1935.

Filed July 9, 1932 55 v. J f t PI m A ll l llr L! A L, n QHIL q f [I L L, L a IF m J L 4 l 11:. 1 F w l Ill T I I: IL

Patented Feb. 12, 1935 PATENT OFFICE PROCESS OF REDUCING SUGARS TO ALCOHOLS Henry Jermain Creighton, Swarthmore,

Pa., as-

signor to Atlas Powder Company, Wilmington, Del., a corporation of Delaware Application July 9, 1932, Serial No. 621,740

29 Claims.

This invention relates to improvements in processes for electrolytically reducing sugars or composite sugar bearing mixtures to polyhydric r alcohols in neutral or alkaline solutions, said solutions rendered capable of conducting electric current, along the line suggested in my patents, Nos. 1,612,361 and 1,653,004 and to improvements in apparatus for carrying out my improved process.

In the process covered by the above mentioned patents, I reduce sugars to their corresponding alcohols in neutral or alkaline aqueous solutions, which are rendered conductive by the addition of suitable electrolytes, in a diaphragm cell employing lead or lead dioxide anodes and a mercury cathode which is agitated.

While the process as described in the above mentioned patents was a decided improvement no over the prior art and gave satisfactory results on a small scale, yet when the cell was enlarged in order to obtain a greater production capacity it was found that the process had certain inherent disadvantages which did not make it amenable for commercial production. A commercial process for the electrolytic reduction of sugars in cells employing a mercury cathode requires a large capital investment for mercury. Furthermore, a mercury cathode must be agitated vigorously in order to effect reduction of the sugar. Effective agitation of a large body of mercury. such as would be required in a commercial mercury cathode cell of this type, was found to be a difficult and costly operation. Also, since mercury is a liquid, this metal, when used as an electrode in an electrolytic cell of this type, can be placed in only one position in the cell, i.e. on the bottom. Therefore an exceedingly large floor space would be required in a commercial plant employing a mercury cathode for the electrolytic reduction of sugars. Cooling of the catholyte in this type of cell has been found to be a difficult and expensive operation.

New I have improved my process and have overcome the inherent disadvantages of the process described in my above mentioned patents. I have reduced the amount of mercury required to an almost negligible quantity. In my improved process it is not necessary to agi- 50 tate the cathodes. I have developed a very compact cell and have reduced the floor space to a small fraction of that required by the mercury cathode cell. I have been able to effect efllcient cooling in my new and improved process.

In its broadest aspect, the present invention resides in the process of reducing sugars, in nonacid solutions capableof conducting electric current, in a cell the cathode or cathodes of which consist of a solid metal plate or plates amalga- T mated with mercury. This solid metal may be in the form of a plate, perforated plate, cylinder, tube, rod or screen.

Lead plates amalgamated with mercury are deemed to be of particular importance in this relation, because extensive practice of the invention with such lead plates has demonstrated their great desirability and adaptability to commercial production in the relation indicated, from the standpoint of high yields andgreat economies in initial cost and in operation, all as more particularly, hereinafter, set forth.

The present invention is a continuation in part of my co -pending application, Serial No. 418,613, filed Jan. 4, 1930, for process of and apparatus for carrying out electrolytic reductions, and while the drawing of the present application is dissimilar in appearance from the drawing of my co-pending application, the principles involved in the two applications are the same insofar as the use of cathodes amalgamated by mercury, in contra-distinction to liquid mercury cathodes, in u the reduction of sugars, is concerned. One advantage flowing from this change in the form of the cathode from liquid mercury cathode to amalgamated cathode is that a plurality of alcohols'may be secured from a single sugar as the result of the reduction process and without other change in cell or conditions.

In the accompanying drawing,

Figure 1 is a diagrammatic plan view of an electrolytic reduction apparatus, hereinafter described.

Figure 2 is a fragmentary longitudinal sectional view therethrough on line 2-2 of Fig. 1, and

Figure 3 is a fragmentary vertical sectional view therethrough on line 33 of Fig. 1.

In the drawing, 5 designates a receptacle constituting a battery cell. This receptacle may be of earthenware. Disposed within this cell are a plurality of rectangular porous diaphragms, 6. These diaphragms may be of alundum, such as the Norton Companys I'M-78 grade. Within these diaphragms are disposed the anode plate 7 which, like the anode of my co-pending application No. 418,613, may consist of chemical lead, or lead that is coated with lead dioxide.

The cathode plates are indicated at 8, and these plates are composed of any suitable metal amalgamated with mercury. As before stated, amalgamated chemical lead plates are preferably employed. These plates'are supported from the end walls of the cell, or in any suitable way. and the solution, containing the sugar being reduced, is discharged into proximity with the faces of these plates by distributor pipes 9 that are disposed upon opposite faces of the plates and are provided with a series of openings in their length. These distributor pipes may be of hard rubber.

These distributor pipes are fed from the transverse feed pipes 10 to which the solution is supplied from a pump of any suitable construction, indicated at 11. The transverse feed pipes may also be of hard rubber. The pump may be a hard rubber gear pump. This pump draws its supply through pipe 12 from the bottom of a vat 13 to which the solution flows through pipes 14 from,

the upper level of the liquid in cell 5. Pipes 12 and 14 may be of hard rubber. Vat 13 may be of earthenware. The vat 13 contains a cooling coil 15 through which any suitable cooling medium. such as water, may be circulated by pump 16. Cooling coil 15 may be of chemical lead and may be shunted to the cathode to prevent itfrom becoming anodic. The pump 16 may be an ordinary iron pump. The source of supply of the cooling medium is immaterial; this arrangement being shown merely to diagrammatically indicate that means are provided for temperature control of the solution. It is immaterial from the standpoint of the invention whether the cell be of the form herein illustrated, or whether it be of the form shown in my application Serial No. 418,613, since the inventive thought, in its broadest aspects, resides in the use of the amalgamated metal cathode for use in the reduction of sugars to polyhydric alcohols. I a

Although I have shown the cell and vat to be of earthenware, the pump circulating the catholyte to be of hard rubber, the distributor pipes also to be of hard rubber, the diaphragms to be of alundum, the anodes to be of chemical lead or lead coated with lead dioxide; I wish it to be understood that any other suitable material may be used for these mentioned parts of the apparatus without departing from the spirit of the invention, because, as has been stated before the inventive thought in its broadest aspects resides in the use of amalgamated metal cathodes for use in the reduction of sugars to polyhydric alcohols.

So far as I am aware I am the first, to utilize a cell of this character in the treatment of sugar solutions, and I have found, as before stated, that marked increases in yield, economies in operation,

and reduction in initial cost, may be achieved by the .use of the amalgamated lead cathodes in lieu of the liquid mercury cathode of my patents above referred to.

There is another important technical advantage for amalgamated lead cathodes over the liquid mercury cathode in that with the amalgamated lead cathode the catholyte is always in an alkaline condition, whereas with a mercury cathode the catholyte often becomes acid, with such consequent decrease in the rate of reduction as to render necessary the addition of alkali by the operator. With the amalgamated lead cathode, it is not necessary to add alkali during the cell operation in order to maintain the catholyte in an alkaline condition. Further, when employing amalgamated lead cathodes the pH value of the solution is easily maintained within those ranges where isomerization of the sugar takes place and as a result I can obtain a plurality of polyhydric alcohols by the use of a single sugar and particularly I can obtain both mannite and sorbite from glucose. When employing a liquid mercury cathode the pH of the solution does not attain a value sufliciently high to cause appreciable isomeriza- From an economic standpoint it is desirable to produce this polyhydric alcohol from glucose which is available in large quantities at low cost. By employing a cell in which the cathodes are metallic plates amalgamated with mercury, I am able to obtain sorbite and an appreciable quantity of mannite by the use of the single sugar, glucose. But when reducing glucose in a mercury cathode cell only the polyhydric alcohol, sorbite is obtained and no mannite.

I can obtain mannite in a mercury cathode cell by reducing inverted sucrose. However, on reducing inverted sucrose in an amalgamated lead cathode cell the yield of mannite is much larger than obtained in the mercury cathode cell.

Of course, mannite can be obtained by reducing mannose in a mercury cathode cell. Mannose is obtained by the hydrolysis of vegetable ivory. The commercial preparation of mannose suitable for electrolytic reduction is a diflicult and expensive operation.

Therefore, the amalgamated lead cathode cell has the added advantage over the mercury oathode cell in that mannite can-be obtained in much greater quantities from sugars which are available in large quantities at low cost.

Sugars that may be used and the alcohols which may be produced from them in the cell described herein are:

Glucose produces manite and sorbite Fructose (levulose) produces manite and sorbite Mannose produces manite and sorbite Galactose produces dulcite and talite Sorbose produces sorbite and idite Xylose produces xylite and arabite Arabinose produces arabite and adonite While I have reduced glucose and fructose in the herein described process, I have found it advantageous, at times, to reduce the mixture of these sugars. A convenient source of such a mixture is invert sugar, which is prepared by the hydrolysis of sucrose. Also, I may produce other mono-saccharides or mixtures of mono-saccharides, to be reduced, by the hydrolysis of other diand poly-saccharides. For example:

Lactose on hydrolysis produces galactose and glucose.

Maltose on hydrolysis produces glucose.

Starch on hydrolysis produces glucose.

Mannan on hydrolysis produces mannose.

Xylan on hydrolysis produces xylose.

By suitably controlling the pH of the catholyte I can obtain one or more polyhydric alcohols by the reduction of analdose sugar. The relative proportion of the two alcohols resulting from such reduction can be controlled by controlling the pH. I may maintain the pH of the catholyte between 7.0 and 13.0; the exact degree varying with the nature of the work being done. For example, when reducing glucose to sorbite, I find that the best results are secured by maintaining the pH value from -100. When reducing glucose to mannite and sorbite. I find it advantageous to maintain the alkalinity of. the electrolyte at a pH value above 10.0. Also, when reducing invert sugar it is desirable to maintain the pH value above 10.0 in order to obtain the maximum yield of mannite. This accurate control of the pH of the catholyte, whereby I can control the relative proportions of the polyhydric alcohols produced, is possible with the amalgamated metal plate cathode cell in a way that would be wholly impossible in the liquid mercury cathode cell.

Further, the plates present much greater areas to the electrolyte than is presented by the liquid mercury cathode of my prior patents. Furthermore, I am able to place the amalgamated plate cathodes much closer to the diaphragm than was practically possible with the liquid mercury cathode. This results in a lower voltage and hence lower power cost.

With respect to the degree of sugar concentration I may state that I have found an initial sugar concentration of 325 grams per liter of the catholyte to be satisfactory from the standpoint of current efllciency and hence power cost. However, concentration of 150 .to 350 grams per liter of catholyte will yield satisfactory results from the standpoint of both current efficiency and resultant power cost.

It will be observed that the use of coil 15 provides a temperature control for the catholyte and this also is found to be of advantage in securing maximum economies of operation. When I reduce sugars in solutions having a low alkalinity, i. e. pH of 7.0 to 10.0 I find that I am able to use a relatively high temperature without seriously effecting the yield of polyhydric alcohols. The higher temperature is advantageous in that the electrical resistance of the solution is decreased and this results in a lower voltage and hence lower power cost. However, when I maintain a high alkalinity in the catholyte, pH 10.0 to 13.0 I am not able to use such high temperatures because with this high degree of alkalinity the sugars and polyhydric alcohols are destroyed at these higher temperatures. Thus, the saving in power cost is more than offset by the loss in yield. Therefore, when reducing sugars employing a catholyte of high pH it is more economical to use lower temperatures. By means of temperature control I am able to balance my operation to obtain maximum economies in operation.

While I have described specific means by which my improved process can be carried out, it is to be understood that the invention is not limited to the use of any particular type of apparatus, but is intended to cover the use of any type of cell employing a cathode consisting of a metal coated or amalgamated with mercury and adapted for use in electrolytic reduction of sugars or composite sugar bearing mixtures to polyhydric alcohol.

While I have described the production of polyhydric alcohols by using a mono-saccharide or mixtures of same and have given certain examples of these sugars, I wish it to be understood that I do not limit myself to these particular sugars but include all of the mono-saccharides which occur in nature as such and those which are produced by the hydrolysis of diand polysaccharides.

As indicative of one way of carrying out the process I- give the following detailed example:

Plates of 10 pound chemical lead were used as cathodes. These were washed with dilute nitric acid and then amalgamated by rubbing pure mercury (free from other heavy metals) on their surfaces. The mercury was rubbed well into the plates. When the amalgamation of the cathodes has been completed they have a bright. shiny surface. They feel greasy to the touch. Also when mercury was poured onto the plates it would flow evenly over the entire surface. The cathodes were then placed in the cell as shown in Fig. 1. The diaphragms, the anodes, the circulating pump together with the feed lines and distributor pipes, the cooling vat and cooling coil were assembled as shown in Fig. 1. The anolyte consisting of an aqueous solution containing 200 grams of sulphuric acid per literwas poured into the diaphragm compartments. The catholyte consisting of an aqueous solution containing the following:

Grams per liter Glucoseui 325 Sodium sulphate (NaaSO4) was introduced into the cathode compartment, and into the cooling vat. The circulating pump was started. The catholyte was recirculated at a rate of about 10 times an hour. As some su1-' phuric acid had seeped into the catholyte from the anode compartment sufllcient sodium hydroxide was added-to bring the catholyte to a pH of 7.0. The volume of catholyte used was 1 liter for every 1.25 sq. dm. of effective cathode surface. The cathodes were connected to the negative pole of a direct current generator while the anodes were. connected to the positive pole of the generator. The current was turned into the cell employing a current density of 1 ampere per square decimeter of effective cathode surface. The pH of the catholyte soon rose to a value of 10.0. The alkalinity of the catholyte increased automatically during reduction. When the concentration reached 17 grams NaOH per liter it was kept at that concentration by adding sulphuric acid (concentration 600 grams H2SO4 per liter) as required. The pH value of the catholyte containing 17 grams NaOH per liter was 12.6. The temperature" of the catholyte was maintained at 20 C. The electroyltic reduction was continued until an analysis showed the disappearance of of the original reducing sugar.

While I have described my process in considerable detail in order that a full disclosure of the invention may be made, I wish to emphasize again that the invention is not limited to any particular type of apparatus but that it includes within its purview whatever changes fairly come within the terms or the spirit of the appended claims.

Having described my invention, what I claim is:

1. The herein described process consisting of the electrolytic reduction of a non-acid electrically conducting aqueous mono-saccharide solution as the catholyte in an electrolysis cell, the oathode of which is a solid body of metal amalgamated with mercury, which also serves to maintain the catholyte in an alkaline condition.

2. The herein described process consisting of the electrolytic reduction of a non-acid electrically conducting aqueous mono-saccharide solution as the catholyte in an electrolysis cell, the cathode of which is a metal plate amalgamated with mercury, which also, serves to maintain the catholyte-in an alkaline condition.

3. The herein described process consisting of the electrolytic reduction of a non-acid electrically conducting aqueous mono-saccharide solution as the catholyte in an electrolysis cell, the cathode of which is a lead plate amalgamated with mercury, which also serves to maintain the catholyte in an alkaline condition.

amalgamated with mercury, which serves to maintain the catholyte in an alkaline condition.

6. The herein described process consisting of the reduction of mono-saccharides in aqueous non-acid electrically conducting solutions to polyhydric alcohols as the catholyte in an electrolysis cell, the cathode of which is a solid metal amalgamated with mercury, which also serves to maintain the catholyte in an alkaline condition.

7. The herein described process for the reduction of mono-saccharides to polyhydric alcohols which consists of electrolytically reducing an aqueous non-acid electrically conducting monosaccharide solution in an electrolysis cell which is divided into anodic and cathodic sections by means 01' porous diaphragms and wherein the cathode is a solid body of metal amalgamated with mercury, which also serves to maintain the catholyte in an alkaline condition.

8. The herein described process for the reduction of mono-saccharides to polyhydric alcohols which consists of electrolytically reducing an aqueous non-acid electrically conducting monosaccharide solution in an electrolysis cell which is divided into anodic and cathodic sections by means of porous diaphragms and wherein the cathode is a solid body of lead amalgamated with mercury, which also serves to maintain the oatholyte in an alkaline condition.

9. The herein described process for the reduction of mono-saccharides to polyhydric alcohols which consists of electrolytically reducing an aqueous non-acid-electrically conducting monosaccharide solution in an electrolysis cell which is divided into anodic and cathodic sections by means of porous diaphragms and wherein the cathode consists of a lead plate amalgamatedwith mercury, which also serves to maintain the catholyte in an alkaline condition.

10. The herein described process of reducing a single aldose to a plurality of polyhydric alcohols which consists of electrolytically reducing an aqueous solution of the same as the catholyte in an electrolysis cell, the cathode of whichponsists of a solid body of lead amalgamated with mercury, while maintaining the pH value above 10.0.

11. The herein described process which consists of the production 01 manniteand sorbite i'rom mannose by electrolytically reducing anaqueous solution of mannose as the catholyte in an electrolysis cell, the cathode of which consists of a solid metal amalgamated with mercury, whole maintaining the pH value of the solution above 10.0.

12. The herein described process of producing mannite and sorbite from fructose which consists of electrolytically reducing an aqueous solution of fructose as the catholyte in an electrolysis cell, the cathode of which consists of a solid body of metal amalgamated with mercury, which also serves to maintain the catholyte in an alkaline condition.

13. The herein described process of producing sorbite and idite from sorbose as the catholyte which consists of electrolytically reducing an aqueous solution of sorbose in an electrolysis cell, the cathode of which consists of a solid body 01 metal amalgamated; with mercury, which also serves to maintain the catholyte in an alkaline condition.

14. The herein described process which consists of electrolytically reducing an aqueous solution of a mono-saccharide as the catholyte in an electrolysis .cell having an amalgamated lead cathode, which serves to maintain the catholyte in an alkaline condition, and maintaining the solution at a pH value of from 7.0 to 10.0.

15. The herein described process of reducing a mono-saccharide to polyhydric alcohols which consists of preparing a mono-saccharide aqueous solution capable of conducting electricity and treating such solution as the catholyte in an electrolysis cell having a solid amalgamated metal cathode whfle maintaining the pH of the catholyte above 10.0.

- 16. The herein described process 01' reducing a mono-saccharide to polyhydric alcohols which consists of preparing a mono-saccharide aqueous solution capable of conducting electricity and treating such solution as the catholyte in an electrolysis cell having a solid amalgamated lead cathode while maintaining the pHot the catholyte above 10.0.

17. The herein described process of reducing glucose to mannite and sorbite consisting of treating an aqueous solution oI-glucose as the catholyte in an electrolysis cell having a solid amalgamated lead cathode while maintaining the alkalinity of the solution at a pH valueabove 10.0.

18. The herein described process of reducing glucose to mannite and sorbite consisting of treating an aqueous solution of glucose as the catholyte in an electrolysis cell having a solid amalgamated metal cathode while maintaining the alkalinity of the solution at a pH value above 10.0.

19. The herein described process consisting of the electrolytic reduction 01' an aqueous solution oi! an invert sugar as the catholyte in an electrolysis cell having a solid amalgamated metal cathode which also serves to maintain the catholyte in an alkalinecondition.

20. The herein described process consisting of the electrolytic reduction of an aqueous solution of an invert sugar as the catholyte in an electrolysis cell having a solid amalgamated lead cathode which also serves to maintain the catholyte in an alkaline condition.

21. The herein described process which consists of reducing a mono-saccharide in a nonacid electricallyconducting'aqueous solution said solution having an initial concentration of from 150 to 350 grams of mono-saccharide per liter as the catholyte in an electrolysis cell, the cathode of which is a solid body of metal amalgamated with mercury which also serves to maintain the catholyte in an alkaline condition.

22. The herein described process which consists of reducing a mono-saccharide ma nonacid electrically conducting aqueous solution said solution having an initial concentration of from 150 to 350 grams of mono-saccharide per liter as the catholyte in an electrolysis cell, the cathode 01' which is a solid body of lead amalgamated with mercury which also serves to maintain the catholyte in an alkaline condition.

23. The herein described process which consists of reducing a mono-saccharide in a nonacid electrically conducting aqueous solution said solution having an initial concentration of from 150 ta 350 grams of mono-saccharide per liter as the catholyte in an electrolysis cell, the cathode of which is a solid body of metal amalgamated with mercury while maintaining the pH of the catholyte above 10.0.

24. The herein described process which consists of reducing a mono-saccharide in a nonacid electrically conducting aqueous solution said solution having an initial concentration of from 150 to 350 grams of mono-saccharide per liter as the catholyte in an electrolysis cell, the oath- -ode of which is a solid body of lead amalgamated with mercury while maintaining the pHof the catholyte above 10.0.

25. The herein described process of reducing a single ketose to a plurality of polyhydric alcohols which consists of electrolytically reduc ing an aqueous solution of the same, as the oatholyte, in an electrolysis cell, the cathode of which consists of a solid body of lead amalgamated with mercury which serves to maintain the pH value of the catholyte above 7.0.

26. The herein described process comprising the reduction of one or more hexoses to one or more polyhydric alcohols which consists of electrolytically reducing an aqueous solution of the same as the catholyte in an electrolysis cell, the cathode of which consists of a solid body of lead, amalgamated with mercury, which serves to maintain the pH value of the catholyte above 7.0.

27. The herein described process of reducing a pentose to one or more polyhydric alcohols, which consists of electrolytically reducing an aqueous solution of the same as the catholyte in an electrolysis cell, the cathode of which consists of a solid body of lead amalgamated with mercury, which serves to maintain the pH value of the catholyte above 7.0.

- 28. The herein described process of reducing glucose to sorbite, which consists of subjecting an aqueous solution or such glucose to the action of, and as the catholyte in an electrolysis cell, having a solid amalgamated metal cathode which serves to maintain the catholyte at a pH value of 7.0 to 10.0.

29. The herein described process of reducing glucose to sorbite, which consists of subjecting an aqueous solution of such glucose to the action of, and as the catholyte in, an electrolysis cell having a solid amalgamated lead cathode which serves to maintain the alkalinity of the catholyte at a pH value of 7.0 to 10.0.

HENRY JERMAIN CREIGHTON.

.Batnt No 1,990,5 2.

OERTIFICATEOF CORRECTION. d February 12, 1935. HENRY JERMAIN cREIGHToN. v Itia hereby certified that error appears in the" printed spec'iifio ation of the above numbered patent requiring correction as follows Page 2, second column, lines 3,- 9 'and m, for "mnite' read mannite; line 72,4atrike out the periodafter "-sorbite" and insert instead a (mum; page 5, first column; line 1;, for--"t a" read to; and that the said- Letters Patent should be read with this correction therein that the same may conform to the record or the case in the? Patent Office;

- Signed arxi sealed this 28th day of June, A. n. 1958.

Henry Van Ar'sdale (Seal) Acting Commissioner of Patent s. 

